Steam turbines, which are used for the local supply of power and can be considered an embodiment of a turbomachine, are relatively large and are thus accordingly heavy. Such steam turbines can weigh well over 100 tonnes. A steam turbine essentially comprises a rotatably mounted component, also referred to as a shaft. This shaft comprises rotor blades which are arranged fixed to the shaft surface. Such a shaft is rotatably mounted inside a casing, wherein the casing comprises guide vanes which, together with a rotor blade, represent a turbine stage.
In operation, the shaft of a steam turbine rotates preferably at 50 Hz or 60 Hz. Such high rotational frequencies lead to enormous centrifugal forces on the rotor blades. In particular, the end stages of a low-pressure steam turbine are accordingly large and thus experience a particularly large centrifugal force.
For technical reasons, the shafts of the steam turbines are operated at a constant rotational speed. In order to nonetheless be able to build relatively large end stages, lower-density materials—which therefore experience smaller centrifugal forces—are used. An example of such a material is titanium, which is used in some end stages. Other solutions may be possible, such that the fixed rotational frequency is reduced, e.g. a half-speed rotational frequency. It would also be possible to reduce the rotational frequency using transmission machines.